A device to device proximity service (D2D ProSe) has become a research subject for a Long Term Evolution (LTE) system.
In a process of designing a physical layer of the D2D ProSe, two major aspects may be classified from a design perspective: discovery signal design, and direct-connection communication design. An objective of the discovery signal design is to enable a user equipment (UE) to identify UEs existing nearby in a network environment. The discovery signal design includes discovery signal sending and discovery signal receiving. An objective of the direct-connection communication design is to design a direct-connection communication procedure between UEs, including a series of procedures such as call initiation, channel sounding, channel feedback, resource scheduling, data transmission, and call completion.
When a UE receives a discovery signal or a direct-connection communication signal, the UE needs to perform channel estimation by using a reference signal, to perform subsequent demodulation and decoding processing.
Therefore, how to implement reference signal transmission in D2D communication needs to be resolved urgently.